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United States Patent |
6,150,739
|
Baumgartl
,   et al.
|
November 21, 2000
|
Circuit configuration for supplying power to electronic tripping device
Abstract
A circuit configuration for supplying power to electronic tripping devices
from a current-transforming device. A switched-mode power supply unit, in
particular a choke/step-up transforming device having a pulse-width
voltage control, is connected downstream of a charging capacitor. Once a
set point of the output voltage at an output capacitor is reached, only a
very high pulse duty factor is provided. Particularly, maximum power point
control is provided during an initial charging phase. Circuit
configurations of this kind serve the power supply of overvoltage tripping
devices in low-voltage and medium-voltage systems.
Inventors:
|
Baumgartl; Ulrich (Berlin, DE);
Rohl; Wolfgang (Berlin, DE)
|
Assignee:
|
Siemens AG (Munich, DE)
|
Appl. No.:
|
147998 |
Filed:
|
March 24, 1999 |
PCT Filed:
|
September 24, 1997
|
PCT NO:
|
PCT/DE97/02215
|
371 Date:
|
March 24, 1999
|
102(e) Date:
|
March 24, 1999
|
PCT PUB.NO.:
|
WO98/13918 |
PCT PUB. Date:
|
April 2, 1998 |
Foreign Application Priority Data
| Sep 24, 1996[DE] | 296 17 365 |
| Sep 24, 1996[DE] | 296 17 367 |
Current U.S. Class: |
307/130; 323/222; 361/93.6 |
Intern'l Class: |
H01H 047/00 |
Field of Search: |
307/130,85,31
323/222,282,284,288
361/93.6
|
References Cited
U.S. Patent Documents
4992723 | Feb., 1991 | Zyistra et al. | 323/284.
|
Foreign Patent Documents |
0 206 253 | Jun., 1986 | EP | .
|
0 206 253 | Dec., 1986 | EP.
| |
0 130 254 | Sep., 1988 | EP.
| |
32 46 329 | Jun., 1984 | DE.
| |
06 202745 | Jul., 1994 | JP.
| |
Other References
Markus Niebauer et al., "Solarenergie Optimal Nutzen Intelligentes
MPP-Tracking Mit Einen ST62-Mikrocontroller", Elektronik, No. 16, Aug. 6,
1996*.
|
Primary Examiner: Ballato; Josie
Assistant Examiner: DeBeradinis; Robert L
Attorney, Agent or Firm: Kenyon & Kenyon
Claims
What is claimed is:
1. A circuit configuration for supplying power to an electronic tripping
device, comprising:
a current-transforming device, a rectified output voltage of the current
transforming device being fed to a charging capacitor;
a switched-mode power supply unit connected downstream from the charging
capacitor for voltage control, the switched-mode power supply unit
including a diode, a switching transistor, and a pulse modulation circuit,
the diode charging an output capacitor connected in parallel to the
electronic tripping device, the switching transistor controlling the
charging of the output capacitor, the pulse width modulation circuit
controlling the switching transistor, the pulse width modulation circuit
controlling the switching transistor at a very high pulse duty factor when
a set point of an output voltage at the output capacitor is reached; and
a maximum power point regulator connected to the pulse width modulation
circuit, the maximum power point controlling the pulse width modulation
circuit during an initial charging phase of the output capacitor so that
an optimal operating point of maximum power matching is adjusted.
2. The circuit configuration according to claim 1, wherein the
switched-mode power supply unit is one of a choke transforming device and
step-up transforming device.
3. The circuit configuration according to claim 1, wherein the
switched-mode power supply unit further includes a flyback converter.
Description
FIELD OF THE INVENTION
The present invention relates to a circuit configuration for supplying
power to electronic tripping devices, the circuit configuration having a
current-transforming device, whose output voltage is rectified and can be
fed to a charging capacitor, which provides the electronic tripping device
with power.
BACKGROUND INFORMATION
Circuit configurations of this kind are described in German Patent No. 32
46 329. When an upper voltage limit is reached, the voltage is
short-circuited in such a way that the current of the current-transforming
device no longer flows into the charging capacitor. In this switching
operation, electromagnetic interference fields arise which corrupt the
measurement current, thereby causing erroneous tripping.
European Patent No. 0 130 254 describes relevant tripping device with two
capacitors, which are to be charged by the current-transforming device for
the operation of this device.
SUMMARY OF THE INVENTION
An object of the present invention is to define a circuit configuration for
supplying power to electronic tripping devices, ensuring the lowest
possible influence on the current of the current-transforming device, and,
in addition, limiting the emission of electromagnetic interference fields
to a minimum.
A further object of the present invention is to achieve the quickest
possible charging of a capacitor at a voltage which is just sufficient.
According to the present invention, these objects are achieved by the
following features:
1.1 A switched-mode power supply unit SNT is connected downstream of
charging capacitor CL in the manner of a choke/step-up transforming device
DR or a flyback converter SW (according to the transformer principle),
1.2 The switched-mode power supply unit SNT includes a diode DI for
charging an output capacitor CA, which is connected in parallel with and
functioning as the power supply of electronic tripping device AE,
1.3 The switched-mode power supply unit includes a switching transistor TR
to control the charging of output capacitor CA, the switching transistor
TR being controlled by a pulse width modulation circuit PW,
1.4 The pulse width modulation circuit PW acts in such a way that when the
set point of an output voltage UA at output capacitor CA is reached, then
switching transistor TR can be controlled with a very high pulse duty
factor, i.e., is only blocking for a short moment in each case, and, as a
refinement of the present invention,
1.5 A maximum power point regulator MPP is provided, which is connected
with pulse width modulation circuit PW for controlling purposes,
controlling it from the beginning of charging output capacitance CA so as
to adjust it to optimal power matching (11, 111, . . . ).
By controlling the switching transistor with the pulse width modulation
circuit, a constant current is impressed, as opposed to the usual
constant-current power supply. In fact, as soon as the output voltage at
the output capacitor has reached the set point, the switching transistor
is no longer controlled with a low but with a very high pulse duty factor.
Accordingly, in the case of very high currents of the current-transforming
device, these are led (via the choke/step-up transforming device) through
conductively connected transistor TR in the switched-mode power supply
unit, and only switched through to output capacitor CA via the diode
during the very short opening times of the switching transistor. In the
case of high currents, this operating mode maintains the voltage at the
charging capacitor low, resulting in an approximately constant power input
at a low voltage level. This favors an exact current measurement by the
current transformer. The electronic control assembly of the switched-mode
power supply unit is supplied with the output voltage of capacitor CA,
since the input voltage at the switched-mode power supply unit is too low,
particularly in the case of high currents of the current-transforming
device. The current is measured in a conventional manner at a shunt
resistor, which can also be arranged upstream of the rectifying device if
required.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a first embodiment of a circuit configuration according to the
present invention.
FIG. 2 shows a characteristic of a current transformer, in particular
voltage plotted over current between no load operation and short circuit
and a power dissipation curve.
FIG. 3 shows a second embodiment of a circuit configuration according to
the present invention for quickly charging an output capacitor.
DETAILED DESCRIPTION
The present invention is explained by a first exemplary embodiment shown in
FIG. 1. FIG. 1 shows only the circuit elements which are essential for
understanding the present invention.
The current generated by current-transforming device SW is rectified by
rectifying device GE in a conventional manner and is conducted via the
choke/step-up transforming device DR either to charging capacitor CL, or,
via diode DI, to output capacitor CA, depending on the position of
switching transistor TR. Switching transistor TR is controlled by the
pulse width modulation circuit in such a way that when output voltage UA
at output capacitor CA reaches the set point, the current of
current-transforming device SW is conducted via switching transistor TR to
charging capacitor CL, arriving via diode DI at output capacitor CA only
during the short opening periods of switching transistor TR. In the case
of high currents, the voltage at charging capacitor CL is therefore kept
at a low value, virtually resulting in an approximately constant power
input at a low voltage level.
The current is measured at the shunt resistor in a conventional manner,
which can also be arranged upstream of rectifying device GE if required.
For high measuring accuracy, a low-impedance resistor is particularly
suitable so that the current transformer is nearly short-circuited.
FIG. 3 explains a second refined embodiment for particularly quickly
charging output capacitor CA, on the basis of FIG. 2.
Features 1.1 through 1.4 are also provided in this example embodiment, with
feature 1.5 being added. The feature assists in the rapid charging of
capacitor CA, namely by achieving operational readiness upon (re)closing.
To achieve this objective, a maximum power point (MPP) operation is
carried out, first disregarding the required value of output voltage UA.
For further explanation of the present invention and its refinement,
reference is made to FIG. 2 showing the characteristic of a current
transformer with regard to the curve of voltage and current between
no-load operation and short-circuit, the curves a, b, c and d representing
currents of different magnitude (as a parameter) flowing through current
conductor S, to which the current transformer that is relevant in this
context is coupled as a source. Additionally shown and referred to as H is
the power dissipation curve showing P=const. for the power demand of
tripping device EA and switched-mode power supply unit SNT, both of which
must be supplied with power by current transformer SW. The area to the
right of and above hyperbola H is the working range available for a
circuit according to FIG. 3, which is still to be described, the capacity
of current transformer SW being sufficient for the power supply of
tripping device AE and switched-mode power supply unit SNT within this
working range. The operating point can be freely selected within this
range. The fact that the present invention provides a switched-mode power
supply unit is particularly advantageous in this context, since, according
to one aspect of the invention, output voltage UA at the output of the
switched-mode power supply unit and the input of the tripping device can
optionally be made independent of input voltage UE at the switched-mode
power supply unit, i.e., the output voltage of current transformer SW,
depending on the execution of the switched-mode power supply unit with
regard to its voltage transformation. Voltages UA and UE are decoupled
from each other, for example, in a switched-mode power supply unit,
permitting the invention to be executed with a low input voltage UE.
According to the refinement for achieving the further object of the present
invention of achieving a rapid charging upon switching on, first,
operating point 11, 111, 211, 311 of respective curve a, b, c, d is set,
at which maximum power can be transferred from transformer SW into the
circuit, the power being adjusted optimally in each case. This adjustment
of the operating point occurs here by the accordingly preselected pulse
duty factor mentioned earlier, which heretofore, before the present
invention, was permanently set empirically and/or at the given voltage
UE=UA.
In the present invention, working operation takes place in the
characteristics field of curves a, b, c, d with regard to operating point
U=f (I). As mentioned above, according to the refinement of the present
invention, the charging of output capacitor CA starts at an operating
point on the connecting line of points 11, 111, 211 and 311, depending on
the output power of the current transformer that is available at that
moment. Selecting the operating point on this connecting line optimally
ensures rapid charging of output capacitor CA. This operating point, e.g.,
point 111 for the existing voltage/current relation of curve b, can be
maintained by the functioning of the maximum power point (MPP) control,
which works in a conventional manner according to the principle of
differential shift of operating point and adjustment to the maximum. When
the charging of output capacitor CA is nearly or completely finished, the
MPP control stops working, and the operating point (the output of the
current transformer assumed to remain constant according to curve b) is
shifted on curve b in the direction of arrow 12 to point P.sub.b, which
intersects power dissipation curve H. This occurs by a corresponding,
pulse-width modulator controlled pulse duty factor of transistor TR of
switched-mode power supply unit SNT. The pulse duty factor is considerably
increased in this process, i.e., the transistor blocks only for short
periods in relation to the duration of the keying period.
As can be gathered from FIG. 2, this shift of the operating point is no
longer possible when the current transformer supplies only a small amount
of power so that between curve d and power dissipation curve H, only one
contact point 311 remains as the only possible operating point. However,
even when approaching these low values of voltage and current of the
current transformer, output capacitor CA can still be sufficiently charged
to supply power to the tripping circuit and the switched-mode power supply
unit.
In principle, the operating point can also be shifted to point P'.sub.b of
curve b intersecting hyperbola H, this being the operating point of the
switched-mode power supply unit when the charging of capacitor CA is
completed. Such an adjustment of the operating point, however, is
disadvantageous for measuring the current flowing through the conductor
with regard to the current transformer that is to be used to carry out
this measurement. As mentioned above, it is advantageous to perform the
current measurement using a current transformer termination having the
lowest possible resistance, i.e., in the range of low output voltage of
the current transformer (=low input voltage of the switched-mode power
supply unit) and high output current of current transformer SW.
For the sake of completeness, it should be pointed out that in the event
that only a step-up transformer is provided in the switched-mode power
supply unit, only that portion of the range above hyperbola H in the
diagram of FIG. 2 is available for selecting the operating point, which is
the portion available below the voltage value indicated by Um (for any
current I). This is not a substantial limitation, however, because it may
be eliminated using a switched-mode power supply unit according to the
transformer principle, in particularly a flyback converter.
The block diagram of FIG. 3 is provided to illustrate this refinement. The
reference symbols described in connection with FIG. 1 have the same
meaning in FIG. 3.
FIG. 3 shows a switched-mode power supply unit SNT having a flyback
converter. As a further essential element, this switched-mode power supply
unit SNT includes transistor TR, which is to be controlled by a pulse
width modulation circuit. In accordance with feature 1.5 (above), a
microprocessor MYP having a maximum power point MPP regulator is provided
here, from which switching transistor TR of the switched-mode power supply
unit is controlled in a pulsed manner. Such MPP regulators are known as
electronic components. They work according to the principle of finding out
and adjusting the maximum power matching (with the load resistance) in
each case by continuous variation. In a different context, the article
"Solarenergie Optimal Nutzen" published in Elektronik 16 describes such a
technology, for example, in the utilization of solar energy.
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